The present invention relates to tubing. More particularly this invention concerns a multilayer tube formed of profiled strip.
A multilayer tube formed of profiled strip is known from German patent document 3,441,064. The strip has inner and outer edges, is formed between them with a double-thickness outwardly directed lip defining an outwardly open inner slot, and is bent back under at its outer edge to form an inwardly open outer slot with the outer edge extending backward toward the inner edge. Where two turns of the strip material overlap, the outwardly directed double-thickness lip of each turn is engaged in the outer slot under the bent-back outer lip of the adjacent turn. Thus the turns are locked together and can shift limitedly relative to each other to allow the tube to be bent. What is more the interfit is so tight that the tube can easily be sealed to safely transport gas or liquid under pressure.
The disadvantage of this system is that, when stretched, relatively wide radially outwardly directed openings are formed that can catch and fill with dirt and the like. Furthermore the tube thus formed is at most two layers thick in many locations so it is not strong. The inner surface of the tube is shingled, with overlapping sections that make flow in the tube turbulent.
It is therefore an object of the present invention to provide an improved tube made of profiled strip.
Another object is the provision of such an improved tube made of profiled strip which overcomes the above-given disadvantages, that is which has smooth outer and inner surfaces even when bent or extended, and which is very strong.
A tube made of profiled strip has according to the invention an inner edge, an outer edge parallel to the inner edge and projecting away from the inner edge, a double-thickness outwardly directed inner lip forming between the edges an outwardly open inner slot, and a double-thickness inwardly directed outer lip forming between the inner slot and the outer edge an inwardly open outer slot. The strip is formed into turns centered on an axis with the inner slot of each turn axially slidably receiving the outer lip of the adjacent turn on an inner side and the outer slot of each turn axially slidably receiving the inner lip of the adjacent turn on an outer side.
As a result whether the tube is axially compressed or extended, the outer surface is generally smooth so particles cannot get between the turns. Furthermore at any point along the tube the strip is at least three layers thick, making it possible for the turns to seal well against each other and providing excellent strength. This makes the tube ideal for use passing hot motor-vehicle exhaust gas, as a tight seal and strength are needed for safety.
In accordance with the invention the inner slots are radially outward of the outer slots. In addition the inner edges are radially inward of the outer edges. Each turn is radially outwardly overlain by an outer-edge portion of the turn on the inner side and is radially inwardly overlain by an inner-edge portion of the turn on the outer side.
According to another feature of the invention respective inner and outer parallel helicoidal elastomeric seals flanking the strip between the slots thereof. The strip is formed between the lips with a web extending generally radially of the axis and the seals lie on opposite axial sides of the web.
It is also possible according to the invention to provide a seal compressed against an edge portions. This seal is compressed against an outer-edge portion.